This invention relates generally to optical transceiver apparatus, and more particularly to optical transceiver systems for dynamic boresight systems of advanced attack helicopters.
In advanced attack helicopters, such as the AH-64 Apache, AH-1 and other helicopters, pylons attached to short wing sections of the aircraft are provided for carrying short range, quick response, gun systems. Gun system accuracy in such arrangements is the product of many factors which vary before, during and after combat maneuvers. These factors may include wing bending, mechanical friction between moving parts, backlash from gears, structural vibration, deflection of the airframe, recoil and the like. A greater appreciation for the factors involved may be obtained by reference, for example, to the article "Guns of the Fighter Helicopter" by Frank Colucci, in the publication Defence Helicopter World, August-September, 1989.
Thus, it is necessary to boresight the gun systems for the location where they are typically aimed. This is a tedious, time consuming operation which heretofore was accomplished with ground based sighting arrangements before the helicopter left for a mission. For example, according to U.S. Army statistics, typically it takes three personnel four hours to boresight an AH-64 helicopter and thirteen hours to boresight an AH-1 helicopter. However, aircraft flex, twist and vibration in flight render the continued accuracy of corrections or calibration doubtful particularly when the same are implemented when the helicopter is on the ground. In such ground based boresight systems, external support equipment, such as telescopes, accelerometers, inclinometers, gyroscope platforms and the like, are generally required for such boresighting. This external support equipment is employed to make either physical adjustments to the aircraft or computer bias entries depending upon the nature of the outputs provided by the measuring equipment.
An angular orientation system is taught in U.S. Pat. No. 3,836,258 to Courten et al. This patent describes an angular orientation measuring apparatus in which a split image of a target is produced by a wedge deviation technique. The wedge deviation technique, in addition to being provided with a wedge assembly, can be provided with optical means. Specifically, four lenses are used to produce a split image of a target line reticle carried on a body. The system cannot be used to produce three-axis orientation.
An aircraft alignment system is also taught in U.S. Pat. No. 4,191,471 to Courten et al. Here the boresight axis of armament is aligned using a collimated beam of light. Specifically, a light source is provided on the gunpod, and supplies collimated light to a collimator secured to a transfer jig temporarily secured to the frame of the aircraft which is parked on the ground. The system cannot provide three-axis orientation, and cannot be used for dynamic, in-flight correction.
U.S. Pat. No. 4,808,604 to Bartholet discloses a micropositioning apparatus for a robotic arm which provides a three-axis orientation. The purpose of this apparatus is firstly to determine precise positional information, and secondly, to determine deflection. With this system, five light sources are provided for each of the shoulder-elbow arrangement and the wrist-elbow arrangement, with each arrangement also having an optical detecting system associated therewith having three optical detectors.
With this system each detector array senses target motion along a single axis parallel to the longitudinal motion and can only be mathematically converted to angular motion if the distance between light sources and detectors is precisely known. This occurs since the focussing and cylindrical lens assemblies are affixed to the detector body, thus being capable only of performing a translational measurement, rather than a direct angular measurement. In this manner, roll angle measurement resolution improves with increased spacing between selected light source pairs. The system requires light source activation in a repetitive sequence in a time-multiplexed fashion to determine the direction of deflection. Numerous light sources are also required. Accordingly, this system is not considered to be applicable for boresighting applications on helicopter, gunships or the like.
U.S. Pat. No. 4,804,270 to Miller discloses a multi-axis alignment apparatus in which displacement of a member relative to a reference plane is determined. The apparatus utilizes a transmitter and a receiver spaced apart a predetermined distance. A reference energy beam coaxially passes a light diffraction grating having a ruled surface. The grating passes a zero order portion of the beam through undeviated, and diffracts a multiplicity of beams of first, second, third and higher orders at constant angles to the zero order portion, the angles varying with the frequency of the grating. A coaxial sleeve movably mounts the light diffraction grating to provide a roll zero reference. The zero part of the beam provides the zero reference for pitch and yaw. The first order beams provide zero reference for roll.
However, this apparatus requires the use of a coherent light source to provide high energy and sharply defined zero and first order beams exiting from the constant deviation prisms. Further, by requiring the use of single optical source in the form of an HeNe laser, a ruled grating and deviation prisms to generate three parallel beams of light, it is difficult to obtain precise alignment of each element relative to the entire transmitter sub-system. Still further, the components, including the laser, grating and constant deviation prisms, are relatively expensive. In addition, the use of cylindrical lenses in close proximity to the roll axis detectors, in order to improve roll sensitivity, greatly limits the angular acquistion and measurement of any system employing reasonably sized components.
Other less relevant system which include positional alignment systems are described in U.S. Pat. Nos. 4,306,806 to Barron, 4,330,212 to Miller, 4,560,272 to Harris and 4,792,228 to Haffner.
Thus, for example, U.S. Pat. No. 4,330,212 to Miller is directed to a tri-axis laser alignment system which measures angular displacement of pitch, yaw and roll using multiple laser beams, optical detectors and grating arrangements.
U.S. Pat. No. 4,306,806 to Barron is directed to an angular alignment device using a collimated light source associated with one of two objects and a prism associated with the other of two objects. A viewing screen is provided for viewing images created by the light source and the prism to provide an indication of the relative orientation of the two objects. The resulting two images provide an indication of the relative orientation of the two objects about three mutually orthogonal axes. The apparatus is particularly useful for detecting and correcting changes in the orientation of a gun tube after firing.